[Botan-devel] need sample code for El Gamal Algorithm operations

[Jack Lloyd]

Some sample code is attached. It does basic key generation, encryption
and decryption. Currently you cannot export ElGamal keys in any sort
of PKCS #8 structure as no OIDs have been defined for it that I know
of (I'll rectify this in 1.7.0, I've been assigned an OID arc by the
IANA and will be allocating nodes for RW, NR, and ElGamal key
formats). Until then, if you want to do import export you'll have to
do it manually with the accessors in DL_Scheme_{PublicKey,PrivateKey}

-Jack

On Mon, Mar 19, 2007 at 08:42:38PM -0700, run zhang wrote:
> Would someone post some sample code for El Gamal key generation and enc/dec?  Thanks a lot. 
>    
> 
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#include <botan/botan.h> // for libraryinitalizer, etc
#include <botan/elgamal.h> // for the key info
#include <botan/look_pk.h> // for get_pk_*
using namespace Botan;

#include <iostream>
#include <memory>

SecureVector<byte> do_encrypt(const SymmetricKey& key,
                              const ElGamal_PublicKey& elg_key)
   {
   std::auto_ptr<PK_Encryptor> enc(get_pk_encryptor(elg_key, "PKCS1v15"));
   return enc->encrypt(key.bits_of());
   }

SecureVector<byte> do_decrypt(const SecureVector<byte>& ciphertext,
                              const ElGamal_PrivateKey& elg_key)
   {
   std::auto_ptr<PK_Decryptor> dec(get_pk_decryptor(elg_key, "PKCS1v15"));
   return dec->decrypt(ciphertext);
   }

int main()
   {
   LibraryInitializer init;

   // generate a 2048 bit ElGamal key
   ElGamal_PrivateKey priv_key(DL_Group("modp/ietf/1024"));
   ElGamal_PrivateKey pub_key = priv_key;

   SymmetricKey sym_key(16); // 128 bits, for, eg AES-128

   SecureVector<byte> enc_key = do_encrypt(sym_key, pub_key);
   SecureVector<byte> dec_key = do_decrypt(enc_key, priv_key);

   if(dec_key == sym_key.bits_of()) // check that it worked
      std::cout << "Decrypted plaintext matches original\n";
   else
      std::cout << "Something went wrong, not identical\n";
   return 0;
   }